Clay product and process of preparing same



Patented May 16, 1939 FEQE CLAY PRODUCT AND PROCESS OF PREPARING SAMEtion of Georgia.

No Drawing. Application November 26, 1934, Serial No. 754,841

12 Claims.

My invention relates to an improved clay and method of making it, andalso to a paper coated therewith.

One of the objects of my invention is to produce a clay the particles ofwhich are in such a state as to render the clay particularly desirablefor use in coating paper, and, more particularly, an object of myinvention is to produce a clay, a substantial portion of the particlesof which have a certain size range.

Another object of my invention is to separate the particles of clay ofthe desired size, and more particularly to efiect this separation byproc-' esses such as dispersion or deflocculation, and if necessary tobreak up agglomerates of clay particles by processes such as grinding.

A further object of my invention consists in producing a fibrousmaterial, such as paper, coated with my improved clay admixed with asuitable binder, such as starch or casein. Another object of myinvention is to reduce the amount of binder required.

A further object of my invention consists in producing a clay coatedpaper with a high finish and a high quality from the viewpoint of color,

i. e., white.

Another object of my invention is to produce a substitute for satinwhite and a paper coated with this material, whereby the clay coatedpaper will approximate in its finish qualities a paper coated with satinwhite.

Further objects of my invention will become apparent as the descriptionof it proceeds.

In the prior art it has been known to coat paper with mineral materialssuch as clays, satin white, calcium carbonate, etc., admixed withsuitable binders, such as starch, casein, glue, etc. The mineralmaterial may be applied to the paper by any of a number of knownmechanical procedures. It may be applied near the conclusion of thepaper-making operation, before the paper web is completely dry, or itmay be applied after the paper is finished and dried. This coatingproduces a smooth surface on the paper which is desirable in certainprinting operations, particularly half-tone printing.

Paper is distinguished by its color and finish. The finish isindependent of the color, for example, a paper may have a good color anda poor finish and vice versa. The finish is readily apparent to a personskilled in the art but its accurate determination is made by aninstrument known in the art as a glarimeter.

Ordinarily when a high quality paper has been desired, with a highfinish, it has been the more or less general practice to employ satinwhite as an ingredient of the coating composition. Satin white is,however, an artificially made material and relatively expensive.Moreover, satin white requires a relatively large amount of binder ascompared with the amount required when clay is used. For these reasons,it is less economical to use than clay and other materials and thepapers so coated have been relatively expensive to make. Papers coatedwith the clays heretofore available have been regarded as inferior infinish and color to those coated with satin white.

I have discovered a process of treating clay whereby the resultingimproved product may be used as a substitute for satin white and when 1used in a coating will produce a paper of a. finish qualityapproximating that obtainable by using satin white.

More particularly, I have discovered that one of the factors whichcontributes to the finish and color of a clay coated paper is the sizeof the clay particles, and that if the clay is treated so that a largepercentage of clay particles have a size range between .1 and 2 microns,a paper coated with a mixture of this clay product and a suitable binderis superior in color and finish to paper heretofore produced by coatingwith clay, and approximates in finish results the paper obtainable bythe use of satin white.

In producing my clay'product it is very desirable that there should notbe too great a pro-' portion of particles of colloidal size becausematerial of this fineness has little hiding power or opacity and,therefore, detracts from the color. 0n the other hand there should notbe a large amount of particles over 2 microns in size. In carrying outmy invention, therefore, I aim to produce a clay in which a very largepercentage of the particles are under 2 microns in size and yet does notcontain too great a proportion of colloidal material.

In the prior art it has been recognized that minerals used for coatingpaper should consist of particles of a small size and that the presenceof too large size particles in the mineral, for example, .001" orgreater, would produce spots in the sheet and cause other undesirablecharacteristics in the paper. However, when clays are treated to removeonly this coarse grit, a paper results which is not markedly superior incolor or finish to that obtainable in ordinaryelay coated papers, as hasbeen known for some time.

I am not aware, however, of any disclosure that the particular sizerange corresponding to the particles in my clay product is advantageous,

and it is wholly unobvious from any prior art with which I am familiarthat my particular clay product should produce a paper having thesuperior properties recited. Nor has there been any teaching how thisclay may be produced. So far as I am aware, none of the processes of theprior art will produce a clay coated paper with properties comparablewith those possessed by my paper.

My novel clay product may be produced by various procedures. However,these procedures all include, as essential steps, first bringing theclay into a dispersed or defiocculated state in an aqueous suspension,and then, while the clay is in the highly dispersed state in the watersuspension, subjecting it to a separating treatment to effect separationof the coarser particles above the predetermined size range from thesuspension, leaving the finer particles of the desired size range insuspension in the water medium. This finer fraction is then recovered ina suitable state for use in a paper coating composition. For the purposeof increasing the yield of the desired fine particle fraction, it issometimes advantageous to subject the clay to a preliminary grindingtreatment. The exact details of the process will depend upon the natureof the clay available as the raw material, as I will point out later.For example, if the clay already contains a large percentage ofparticles under 2 microns in size, as much grinding may not be necessaryas if the clay consisted primarily of larger particles.

Clays suitable for use in paper making may be employed. In general itmay be stated that it is better to use a soft clay. A soft clay is onein which the lumps can be rubbed out after the clay has become wet andthen dried.

If a soft clay occurs by itself in the deposit it may be taken outseparately and treated. If hard and soft clays occur together, they maybe air separated and the soft clay treated. The size of the originalclay agglomerates is not so important except as it may affect the yieldof particles of the required size and the time required for grinding, ifgrinding is employed as a step in the process. sirable includeGeorgiaclays such as Sandersville and Dry Branch clays.

In some instances the clay may be subjected to my process just as itcomes from the deposit. If the clay is wet, however, as it occurs in thedeposit, (containing over 5% natural moisture) I find it desirable tofirst dry the clay to eliminate the moisture down to at most 5%. This ispreferably effected by air drying and aging, but if weather conditionsdo not permit, then the clay may be subjected to artificial drying. Ihave found that a naturally occurring wet clay, while it may be soft andof an advantageous particle size, does not respond as rapidly to mytreatment as does a dry clay. For example, an English clay which is a.soft wet clay is not improved a great deal by grinding alone. If it isfirst dried, the improvement upon being subjected to my process isremarkable.

In carrying out that form of my process in which the clay is subjectedto grinding, I place a suitable clay in a pebble mill and add to itwater and a deflocculating or dispersing agent. The proportions of clay,water and dispersing agent may vary but I find that a mixture of from 50to 75% clay gives desirable results. The deflocculating agents arepreferably potassium hydroxide and sodium silicate; the latter ispreferred because it is relatively inexpensive and works very The claysI have found particularly desatisfactorily. Others may be used, such aspotassium hydroxide and casein, calcium hydroxide and casein, ammoniaand casein or dextrin or dextrin gums in admixture with ammonia 'orpotash. The amount of dispersing agent varies between 2000 cc. and 6000cc. 40 B. sodium silicate to the ton of clay, depending on the time ofgrinding. If the time of grinding is relatively short, a smaller amountof dispersing agent will be needed than if a. longer grinding period isemployed. I find it desirable to employ a minimum amount of thedispersing agent for the reason that too great an excess, while notaflecting the color or size of the particles, tends to produce a lessdesirable finish.

This mixture is then ground and at the conclusion of the grinding, theslip produced is drawn oflf, diluted with water, and the coarsen claysettled or separated by centrifuging. The object of the grinding is toproduce a high yield of clay, preferably or more consisting of particlesof a size of 2 microns or smaller, but containing as little truecolloidal clay as possible. In practice the percentage may vary somewhaton each side of this figure depending on the clay used and will besmaller if a shorter grinding time is employed. The amount of grindingwill depend somewhat on the properties of the clay and the economicsinvolved. In general it is not economical to grind over three hours, asthe increase in particles of the desired size is out of proportion tothe power consumed, and too many particles of colloidal size may beproduced. An grinding conditions which will fulfill these requirementsare within the scope of my invention, but I have found that a pebblemill, preferably with small pebbles, is desirable. The dilution, aftergrinding and preliminary to separation of the fine fraction, may varyover wide limits but in general I dilute the mixture to about 25%solids. In effecting the separation of the fine fraction, the coarserparticles may be allowed to settle in a tank settler and part or all ofthe grit is thus settled out. This settling may be continued until allof the coarse clay settles, or after a preliminary settling, theremainder of the coarse clay may be separated by centrifuging, forexample, in a Laughlin continuous type centrifuge.

In the prior art, it has been quite common to dilute the slip to alarger extent than I have specifled, i. e., 3% to 20% clay. I havediscovered that by using the higher clay mixture the separation of thecoarse particles may be obtained more quickly when they are separated bysettling and that in case a centrifuge is employed the mixture has theright consistency for the centrifuging operation.

It is not absolutely necessary to have the dispersing or deflocculatingagent in the mixture during the grinding. It should be present, however,in the classifying step to promote the separation of the coarse and fineparticles. For example, I can grind the clay without dispersing, thendisperse and dilute, or dilute and then disperse, and classify. However,by using the dispersing agent during the grinding, the clay has agreater fluidity and this aids in the roll of the pebbles. It alsopermits the use of a higher percentage of clay prise particles at leastabout to 90% of which are of a size less than 2 microns and yet a smallPortion of which is of colloidal size.

This suspended clay is then fiocculated, for example, by the addition oflime or alum. The clay then may be filtered and dried if desired.

If the clay has a sufliciently large percentage of fine particles, andother desirable characteristics, the grinding may be dispensed with. Theparticles of the desired size may be separated by dispersing with adefiocculating agent and settling or centrifuging or both. The use ofthe centrifuge in the separating is optional. It is desirable, however,in any of the variations of my process because it speeds up theseparation and results in a more accurate classification. Ihave found,however, that grinding is one of the factors which improves the color ofthe clay coated paper. I wish it to be understood, however, that myinvention is not limited to a process in which the clay is ground.

According to a specific example, which is recited merely as illustrativeof the general process embodying my invention, one ton of Sandersvilleclay (dry) is placed in a pebble mill with 1000 lbs. of water and 2000cc. of 40 B. sodium silicate. The mill is operated for about one hourand the slip produced is drawn off and diluted with 240 gallons of waterand centrifuged using a Laughlin type continuous centrifuge. Under theseconditions a fine fraction consisting of clay particles Within thedesired size range and amounting to about 40% of the amount of clay willbe obtained. The coarse clay is continuously removed and may be returnedto the pebble mill for further grinding or utilized as a less desirablegrade of clay. The clay of the desired size range remains suspended inthe water and flows out of the centrifuge. This is fiocculated by theaddition of alum or any other fiocculating agent and filtered. The claymay then be dried.

The procedure above described may be modified by employing 6000 cc. of40 B. sodium silicate and by running the pebble mill for three hours.

I may also employ Macon (Georgia) clay and subject it to the,procedurerecited in either of the preceding paragraphs.

After my improved clay is produced by the above described process it ismixed with a binder and applied to paper by methods well known in thepaper coating art. Any of the conventional binders may be used. I havefound, however, that casein is very desirable.

With my clay substitute for satin white I am able to use a much smalleramount of casein than is required when satin white is used and in someinstances amounts as low as 15% will sufiice. In producing a hard sizewith a waterproofing eifect, casein in an amount not over 20% may beemployed. This results in a double saving because my improved clay ischeaper than satin white and the amount of casein needed is less.

While processes of coating paper with clay employing amounts of caseincomparable to that I am enabled to employ are known, such processesapply to ordinary clay in which the particles are of larger size than inmy process and the resulting coated paper is inferior from thestandpoint of finish andcolor to that obtainable by my process.

Where I use the words coating or coated herein, I refer to theapplication of the material to the surface of the paper in any mannerand at any time subsequent to the formation of the paper pulp into aweb, either before or after it has dried.

By "colloidar I refer to particles of a size smaller than .1 micron.

By my process there is produced a finely divided mineral materialadapted for use in place of satin white and consisting of a finefraction of clay containing colloidal and non-colloidal smallerparticles of such size and in such proportions as to impart desirablesurface characteristics of gloss and color when applied to paper. V

While I have described in detail advantageous embodiments of myinvention, it is to be understood that my invention may be variedconsiderably within the limitations required by the disclosures in theprior art without departing from the spirit of my invention or the.scope of the following claims.

I claim:

1. The process of treating Georgia clay to provide a finely dividedmaterial adapted for use in coating paper which comprises mixing theclay with water to form a diluted aqueous suspension, introducing adispersing medium to said suspension to increase the dispersion of theclay, subjecting said suspension to a controlled centrifuging to effecta separation of the clay into a finer suspended fraction containingcolloidal and noncolloidal smaller particles of such size and in suchproportions as to impart desirable surface characteristics of gloss-andcolor when applied to paper and into a fraction containing largerparticles, adding a fiocculating agent to the suspended fraction, andfiltering the fiocculated fraction to provide a finely divided mineralmaterial adapted for use in place of satin white.

2. The process of treating clay' to provide a finely divided materialadapted for use in coating paper which comprises mixing the clay withwater to form a diluted aqueous suspension, introducing a dispersingmedium to said suspension to increase the dispersion of the clay,subjecting said suspension to a precipitating force under controlledconditions to effect a separation of the clay into a finer suspendedfraction containing colloidal and non-colloidal smaller particles ofsuch size and in such proportions as to impart desirable surfacecharacteristics of gloss and color when applied to paper and into afraction containing larger particles, adding a fiocculating agent to thesuspended fraction, and filtering the fiocculated fraction to provide afinely divided mineral material adapted for use in place of satin white.

3. The process of treating clay to provide a finely divided materialadapted for use in coating paper which comprises mixing the clay withwater and with a dispersing agent and bringing the clay into adefiocculated state in an aqueous suspension, subjecting said suspensionto a controlled precipitating treatment to effect a separation of theclay into a finer suspended fraction containing colloidal andnon-colloidal smaller particles of such size and in such proportions asto impart finish characteristics when applied to paper substantiallyequal to those obtainable with satin White and into a fractioncontaining larger particles, and recovering the finer fraction from thesuspension.

4. The process of treating clay to provide a finely divided materialadapted for use in place of satin white in coating paper which comprisesmixing the clay with water and with a dispersing agent and bringing theclay into a defiocculated state in an aqueous suspension, subjectingsaid suspension to a precipitating force under controlled conditions toefiect a separation of the clay into a finer suspended fractioncontaining colioidal and non-colloidal smaller particles of such sizeand in such proportions as to impart desirable finish characteristicswhen applied to paper substantially equal to those obtainable with satinwhite and into a fraction containing larger particles, adding afiocculating agent to the suspended fraction, and filtering theflocculated fraction to provide a finely divided mineral materialadapted for use in place of-satin white.

5. The process of treating clay to provide a finely divided materialadapted for use in place of satin white in coating paper which comprisesmixing the clay with water and with a dispersing agent and bringing theclay into a deflocculated state in an aqueous suspension, subjectingsaid suspension to a precipitating force under controlled conditions toeffect a separation of the clay into a finer suspended fractioncontaining colloidal particles and non-colloidal smaller particles atleast about 80% of which are of a size between 0.1 and 2 microns andadapted to impart desirable surface characteristics of gloss and colorwhen applied to paper and into a fraction containing larger particles,and recovering the finer fraction from the suspension.

6. The process of treating clay to provide a finely divided materialadapted for use in coating paper which comprises mixing the clay withwater and with a dispersing agent and bringing the clay into adefiocculated state in an aqueous suspension, subjecting said suspensionto a controlled centrifuging to effect a separation of the clay into afiner suspended fraction containing colloidal and non-colloidal smallerparticles at least about 90% of which are of asize two microns andsmaller and in such proportions as to impart desirable surfacecharacteristics of gloss and color when applied to paper and into afraction containing larger particles, adding a fiocculating agent to thesuspended fraction, filtering said suspended fraction and recovering thefiocculated fine fraction as a finely divided mineral material adaptedfor use in coating paper.

7. The process of treating clay to provide a finely divided materialadapted for use in coating paper which comprises grinding the clay withwater in the presence of a dispersing agent and bringing the clay into adefiocculated state in aqueous suspension, subjecting said suspension toa precipitating force under controlled conditions to efiect a separationof the clay into a finer suspended fraction containing colloidal andnoncolloidal smaller particles of such size and in such proportions asto impart desirable finish characteristics when applied to papersubstantially equal to those obtainable with satin white and into a.fraction containing larger particles, and recovering the finer fractionfrom the suspension.

8. The process of treating clay to provide a finely divided materialadapted for use in. place of satin white in coating paper whichcomprises mixing the clay with water and a dispersing agent and bringingthe clay into a deflocculated state in an aqueous suspension consistingof about 25% or more clay solids, subjecting said suspension to aprecipitating force under controlled conditions to efiect a separationof the clay into a finer suspended fraction containing colloidal andnon-colloidal smaller particles of such size and in such proportions asto impart desirable finish characteristics when applied to papersubstantially equal to those obtainable with satin white and into afraction containing larger particles, and recovering the finer fractionfrom the 5 suspension.

9. As a product of manufacture, a finely divid-r ed material adapted foruse in place of satin white in paper-coating compositions, consisting ofa clay fraction produced from clay by successively bringing the clayinto a. deflocculated state in an aqueous suspension, subjecting saidsuspension to a precipitating force under controlled conditions toeflfect a separation from said suspension of particles above apredetermined size range, and then recovering the smaller particlesremaining in suspension, said clay fraction comprising the particlesrecovered from said suspension and consisting of colloidal andnon-colloidal smaller particles of which at least about 80% are between0.1 and 2 microns, inclusive, in size, and in such proportions as toimpart desirable suri'ace characteristics of gloss and color when usedin coating paper.

10. As a product 01 manufacture, a finely divided material adapted foruse in place of satin white in paper-coating compositions, consisting ofa clay fraction produced from clay by successively bringing the clayinto a defiocculated state in an aqueous suspension, subjecting saidsuspension to a precipitating force under controlled conditions toefiect a separation from said suspension of particles above apredetermined size range, and then recovering the smaller particlesremaining in suspension, said clay fraction comprising the particlesrecovered from said suspension and consisting of colloidal andnon-colloidal smaller particles at least 90% of which are of a size twomicrons and smaller and in such proportions as to impart desirablesurface characteristics of gloss and color when used in coating paper.

11. A paper product particularly adapted for use in half-tone printingand for similar purposes, having a surface formed by a coatingcontaining a finely divided mineral material consisting of a fine clayfraction substantially identical with that produced by successivelybringing the clay into a defiocculated state in an aqueous suspension,subjecting said suspension to a precipitating force under controlledconditions to effect a separation from said suspension ogm rticles abovea predetermined size range, and then recovering the smaller particlesremaining in suspension, and consisting of colloidal particles andnoncolloidal smaller particles, of which at least 80% are between 0.1and 2 microns, inclusive, in size, and in such proportions as to impartdesirable finish characteristics when applied to paper substantiallyequal to those obtainable with satin white.

12. A paper product particularly adapted for use in half-tone printingand for similar purposes, having a surface formed by a coatingcontaining a finely divided mineral material consisting of a fine clayfraction substantially identical with that produced by successivelybringing the clay into a deflocculated state in an aqueous suspension,subjecting said suspension to a precipitating force under controlledconditions to eifect a separation from said suspension of particlesabove a predetermined size range, and then recovering the smallerparticles remaining in suspension and consisting of colloidal particlesarid non-colloidal smaller particles at least 90% of which are of a sizetwo microns and smaller, and in such. proportions as to impart desirablefinish' characteristics when applied to paper substantially equal tothose obtainable with satin white.

WILLIAM T. MALONEY.

